When costing things out, don't forget the fuel savings coming from most
conversions.  My web site http://my.tbaytel.net/guskers has a spreadsheet
http://my.tbaytel.net/guskers/Mileage2.zip you can play with to take a look
at your potential savings.

I saw 21 mpg fully loaded, water tank full, roof racks loaded, towing a
trailer with my auto 90 Westy (2.0 litre I4 conversion), doing the Lake
Superior north shore (about 1600km return with 7% grades).  I measured 27
mpg flat highway with the empty van.  These values use Imperial gallons.

At current fuel costs it's very easy to rationalize the expense...providing
you really want to keep your vanagon.  If you consider the ongoing expense
of maintaining a vehicle at minimum 15 years old, and if you're labour is
not free, one really has to really question keeping the van at all.  If I
didn't like the Westy so much I never would have gone through the
considerable labour and expense of doing the conversion.